Study 1 was conducted to determine if partial restriction of testicular thermoregulation affects spermatogenesis when compared to full restriction by mild scrotal insulation for 48 h. Study 2 and Study 3 were conducted to investigate the efficiencies of selected semen separation techniques on the removal of abnormal spermatozoa. in Study 1, semen from control and partial scrotal insulation (Pl) bulls did not differ between the pre-insult and post-insult period for any variable measured. Full scrotal insulation (Fl) bulls differed for several variables measured, but at different intervals and for different durations post-insulation. Spermatozoal motility and acrosomal integrity were reduced during Period 3 only of semen collection with no effect on sperm output. Full insulation caused abnormalities to be ejaculated from d 10 to 33 post-insulation. Specific morphologically abnormal cells occurred in a chronological order. The order of occurrence was: tailless heads, diadem defect, nuclear vacuole defect, pyriform shaped heads, protoplasmic droplets, severely misshapened heads, acrosomal abnormalities, and the dag defect. In Study 2, a pooled sample of frozen-thawed semen from FI bulls in Study 1 was separated using swim-up separation, glass wool filtration, Percoll® density gradients (45/90% two-layer and 50/70/90% three-layer), and Sephadex® filtration. Glass wool filtration was basically without effect and will be excluded from further discussion. All other separation techniques improved motility from the initial sample at the expense of spermatozoal harvest. The subtle head abnormalities were unaffected by separation for all techniques and spermatozoa with nuclear vacuoles on normal shaped heads were enriched; however, head abnormalities were removed with increasing frequency as the severity of the head distortion increased. In Study 3, frozen-thawed ejaculates with a high concentration of spermatozoa with nuclear vacuoles (>20%) were separated using 45/90% Percoll® and 45/100% Percoll® density techniques. The greater the number of nuclear vacuoles per sperm head, the more efficient the removal of such sperm. The separation of spermatozoa with subtie head distortion as well as spermatozoa with nuclear vacuoles on normal shaped heads by density separation, would allow further assessment of the importance of these abnormal sperm to decreased fertility and increased embryonic mortality.